Biocatalytic Valorization of Used Soybean Cooking Oil for Furfuryl Esters Production: Effects of Alcohol Feeding Strategy and Water Removal on Immobilized Lipase Performance and Stability

Abstract This study describes an efficient biocatalytic process for the synthesis of furfuryl esters from used soybean cooking oil (USCO). The process involves the hydrolysis of USCO using free Candida rugosa lipase, followed by solvent-free esterification of the resulting free fatty acids (FFAs) with furfuryl alcohol (FA) catalyzed by immobilized lipase Eversa Transform 2.0 (ET2.0). Five supports, including acid-treated rice husks with fine (FRH) and coarse (CRH) particle sizes, commercial and rice husk-derived octyl-functionalized silica, and poly(styrene-divinylbenzene) (PSty-DVB), were evaluated for ET2.0 immobilization by physical adsorption. Among the evaluated supports, PSty-DVB provided the highest immobilized protein loading (31.3 ± 1.1 mg g–1) and the best overall catalytic performance in furfuryl esters synthesis. Using this biocatalyst, FFAs conversion reached approximately 94% within 60 min at 45 °C under solvent-free conditions and with a slight excess of FA (FFAs:FA molar ratio of 1:1.15). The combination of stepwise furfuryl alcohol feeding and molecular sieves for in situ water removal improved biocatalyst operational stability, allowing the retention of approximately 95% of the initial activity after 15 consecutive esterification cycles. These results show that ET2.0 immobilized on PSty-DVB is a suitable biocatalyst for the solvent-free conversion of waste-derived fatty acids into furfuryl esters.